The present invention relates to a tool for chip removing machining comprising a relatively tough core connected to a relatively wear resistant outer periphery, and to methods and apparatus for making the tool.
It is previously known through for example WO 98/28455 to press a core and a surrounding tube of material powder in two steps. The material powder comprises tungsten carbide (WC) together a with cobalt (Co) binder that are compressed between a punch and a die, and that subsequently are sintered such that the binder metal is melted and binds the carbide to form a tool material for chip removing machining. Thus, there results a tube formed around, and connected to, an inner core. The core has a higher binder (cobalt) ratio than does the tube, whereby the core is tougher than the tube, but the tube is harder and more wear resistant than the core.
That known technique brings about a plurality of drawbacks during manufacture of elongated slender bodies. The powder gives off dust, and the formed green body (pressed but not sintered material) will not endure handling to any degree. Furthermore the chip flutes must be formed by grinding which is time consuming. The problems have partly been solved by the injection molding of hard metal mixed in a carrier such as indicated in U.S. Pat. No. 5,947,660. The method of injection molding brings about a high degree of freedom concerning geometry but brings about troubles during manufacture of elongated slender bodies and costly investments in molds.
U.S. Pat. No. 4,779,440 discloses that an extruded drill blank having chip flutes of constant pitch along the circumference of the blank can be obtained by heating a hard metal powder to extrusion temperature, and pressing the heated powder under high energy consumption through a space defined by a mandrel and a nozzle while rotating the blank. The blank is guided during the extrusion step past a helical ridge provided inside of the nozzle, to shape chip flutes along the blank. A drawback of the known technique is that the useful life of the tool is less than desired.
One object of the present invention is to provide a tool, whereby the drawbacks of the known technique are eliminated.
Another object of the present invention is to provide a tool having optimum length of service time.
These and other objects have been achieved by a tool for chip removing machining. The tool comprises a shank having at least one cutting edge at a front end thereof, and a corresponding number of chip flutes for conducting chips generated by the respective cutting edge. A radially central portion of the shank is formed of a first hard material, and a radially outer peripheral portion of the shank is formed of a second hard material. The second hard material is harder and less tough than the first hard material. The radially outer peripheral portion is of sufficient thickness that the at least one chip flute is formed entirely therein.